The diagnosis of ocular infections in animals can be problematic. For example, the diagnosis of feline herpes virus 1 (FHV-1) is typically based on clinical signs and PCR-confirmed presence of viral DNA. However, diagnosis is complicated by the occurrence of false negative PCR results and the fact that a positive PCR result may also reflect low level viral shedding or even latent infection. Therefore, it is often impossible to prove that the observed clinical signs are indeed linked to the presence of FHV-1 DNA. An accurate and quick diagnosis is key to ensure an efficient treatment and to avoid over-medication.
Different antiviral compounds are known for the treatment of herpes virus infections. The compound 2-amino-9-[[(1S,2R)-1,2-bis(hydroxymethyl)cyclopropyl]methyl]-1,9-dihydro-6H-Purin-6-one (also known as “A-5021”) is a potent inhibitor of herpes virus replication (Neyts et al., Antiviral Research 2001, 49, 115-120; Iwayama et al., Antimicr. Agents Chemother. 1998, 42, 1666-1670). For example, A-5021 has been reported to be a potent and selective antiviral agent against herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2 (HSV-2) and varicella-zoster (VZV) in vivo. However, the medical and veterinary use of A-5021 is hampered by its poor solubility. Solubilization of A-5021 to pharmacologically active concentrations is heavily pH dependent, and obtaining a stable solution comprising more than 1 mg/mL of A-5021 (or 0.1% w/v A-5021 solutions) typically requires pH values of either below 4 or above 10. Eye drop compositions having a pH value of about 7 and comprising more than 1 mg/mL A-5021 have been reported by Itahashi et al. (Cornea 2008, 27, 334-338), but these compositions have a poor stability and thus can not be used in practice. Therefore the preparation of stable pharmaceutical formulations of solubilized A-5021 is not straightforward.
There is a need for improved methods of diagnosing viral infections and for compositions which effectively treat (ocular) herpetic infections, which mitigate at least one of the problems stated above.